1. Field of the Invention
The invention relates to a vehicle running control system and a vehicle running control method.
2. Description of the Related Art
A vehicle running control system is proposed as a control system that controls running of a vehicle, such as an automobile. The vehicle running control system changes running control for the vehicle to the one different from normal running control when a driver has quickly depressed or released an accelerator pedal.
There is such a vehicle running control system that varies driving force of the vehicle using a driving force control device on the basis of, for example, an operating speed that is a speed at which a driver operates an accelerator pedal. Specifically, when the driver has quickly depressed or quickly released the accelerator pedal, the vehicle running control system detects a relatively high accelerator pedal operating speed and then controls a power source, such as an engine, to generate driving force having a rate of change higher than a rate of change of driving force generated in normal operation control on the basis of the detected accelerator pedal operating speed. By so doing, when the driver has quickly depressed or quickly released the accelerator pedal, the vehicle running control system is, for example, able to accelerate or decelerate the vehicle at a rate higher than that of the vehicle that is controlled in normal operation control.
As a related art, there is, for example, proposed a vehicle driving force control system that controls driving force of a vehicle on the basis of a rate of change of an accelerator position, that is, an accelerator pedal operating speed (see Japanese Patent Application Publication No. 2003-237421(JP-A-2003-237421)). The vehicle driving force control system described in JP-A-2003-237421 detects a vehicle speed, an accelerator position and a rate of change of an accelerator position to generate a vehicle speed control target driving force and an acceleration control target driving force, and, furthermore, adds the vehicle speed control target driving force and the acceleration control target driving force to generate a target driving force of the vehicle in response to a driver's request.
Incidentally, in general, when the driver operates the accelerator pedal, the accelerator pedal operating speed tends to vary with a stroke amount that is an amount by which the driver operates the accelerator pedal. Therefore, for example, even when the driver does not intend to quickly depress the accelerator pedal, when the driver depresses the accelerator pedal and then the stroke amount of the accelerator pedal becomes relatively large, the accelerator pedal operating speed also becomes relatively high, so large driving force tends to be generated with respect to driving force generated in normal operation control. That is, a driver's intention may not be reflected on running of the vehicle, so there is room for improvement to reflect a driver's intention on running of the vehicle when the driver has operated the accelerator pedal.